Boot

Abstract

A boot of extends along an axis X direction and has a cylindrical shape that is extendable and contractable in the axis X direction. The boot includes a bellows portion alternately having a bellows portion-side peak portion and a bellows portion-side valley portion along the axis X direction, and an extending portion connected adjacent to the bellows portion in the axis X direction and provided adjacent to one end and/or an other end of the boot in the axis X direction. The extending portion is formed so that an outer diameter of an end of the extending portion on a side opposite to a side connected to the bellows portion in the axis X direction is smaller than an inner diameter of the bellows portion-side valley portion of the bellows portion.

The invention claimed is: 
     
         1 . A tubular boot that extends along an axis direction and is extendable and contractable in the axis direction, the boot comprising:
 a bellows portion alternately having a bellows portion-side peak portion and a bellows portion-side valley portion along the axis direction, and   an extending portion connected adjacent to the bellows portion in the axis direction and provided adjacent to one end or an other end of the boot in the axis direction,   wherein the extending portion is formed so that an outer diameter of an end of the extending portion on a side opposite to a side connected to the bellows portion in the axis direction is smaller than an inner diameter of the bellows portion-side valley portion of the bellows portion,   wherein the extending portion is configured so that at least a part of the extending portion is displaced into the bellows portion when the boot is compressed in the axis direction,   wherein the bellows portion is configured to be compressed in the axis direction after at least a part of the extending portion is displaced into the bellows portion when the boot is compressed in the axis direction, and   wherein the boot is configured to have a local minimum restoring force state where a restoring force in the axis direction increases after the restoring force decreases, as a compression ratio increases, between an extended state and a compressed state.   
     
     
         2 . The boot of  claim 1 , wherein the extending portion comprises an extending portion-side peak portion provided adjacent to the bellows portion, an extending portion-side valley portion provided adjacent to the one end or the other end of the boot in the axis direction, and a coupling portion that couples the extending portion-side peak portion and the extending portion-side valley portion, and
 wherein the coupling portion is configured so that at least a part of the coupling portion is displaced into the bellows portion when the boot is compressed in the axis direction.   
     
     
         3 . The boot of  claim 2 , wherein the extending portion is formed so that a length in the axis direction between the extending portion-side peak portion and the extending portion-side valley portion is longer than a length in the axis direction between the bellows portion-side peak portion and the bellows portion-side valley portion. 
     
     
         4 . The boot of  claim 2 , wherein the extending portion is formed so that an outer diameter of the extending portion-side peak portion is smaller than an outer diameter of the bellows portion-side peak portion. 
     
     
         5 . The boot of  claim 2 , wherein the extending portion is formed so as to have a higher rigidity in the extending portion-side valley portion than in other parts of the extending portion. 
     
     
         6 . The boot of  claim 1 , wherein the extending portion is configured to be curved so as to overlap in a radial direction so that a restoring force can act in the radial direction, when the extending portion is compressed in the axis direction. 
     
     
         7 . A tubular boot that extends along an axis direction and is extendable and contractable in the axis direction, the boot comprising:
 a bellows portion alternately having a bellows portion-side peak portion and a bellows portion-side valley portion along the axis direction, and   an extending portion connected adjacent to the bellows portion in the axis direction and provided adjacent to one end or an other end of the boot in the axis direction,   wherein the extending portion is formed so that an outer diameter of an end of the extending portion on a side opposite to a side connected to the bellows portion in the axis direction is smaller than an inner diameter of the bellows portion-side valley portion of the bellows portion,   wherein the extending portion is configured so that at least a part of the extending portion is displaced into the bellows portion when the boot is compressed in the axis direction,   wherein the extending portion comprises an extending portion-side peak portion provided adjacent to the bellows portion, an extending portion-side valley portion provided adjacent to the one end or the other end of the boot in the axis direction, and a coupling portion that couples the extending portion-side peak portion and the extending portion-side valley portion,   wherein the coupling portion is configured so that at least a part of the coupling portion is displaced into the bellows portion when the boot is compressed in the axis direction, and   wherein the boot is configured to have a local minimum restoring force state where a restoring force in the axis direction increases after the restoring force decreases, as a compression ratio increases, between an extended state and a compressed state.